MON-135 Pituitary Adenoma Presenting with Gynecomastia

Abstract Disclosure: S. Perabattula: None. S. Yavuz: None. R. Pradhan: None. Abstract: Background: Pituitary macroadenomas, can compress the pituitary gland or stalk, disrupting gonadotropin-releasing hormone (GnRH) input from the hypothalamus or directly impairing luteinizing hormone (LH) and follicle-stimulating hormone (FSH) secretion. This leads to central (secondary) hypogonadism. The hormonal imbalance, particularly the reduced testosterone-to-estrogen ratio, promotes breast tissue growth in men. Case: A 42-year-old cis male presented to the endocrine clinic in July 2024 for breast enlargement for 9 months, tender to touch with no active breast discharge. He also reported decreased morning erections but no change in libido. Normal facial hair, no shift in shaving pattern. History includes hypothyroidism on levothyroxine 100 mcg; and OSA on CPAP. Initial labs of total testosterone-8 ng/dL [250-1100 ng/dL], free testosterone-1.4 pg/mL [35-155 pg/mL], TSH-2.64 [0.27-4.2 mU/L], free T4-0.6[0.9-1.7 ng/dL], LH 0.87[1.3-8MIU/ml], estradiol 11.8[11.3-43.2 pg/ml], prolactin 31.7 [4-15.2 ng/ml] Subsequent workup showed: mammogram: bilateral gynecomastia with no suspicious mass and an MRI brain showed a pituitary macroadenoma measuring 2.8 X2.7X 2.6 cm heterogenous enhancing mass enlarging the sella, with mild mass effect on the optic chiasm. Labs: IGF-I:66[52-328 ng/ml]; a.m. cortisol-8.2[4.8-19.5ug/dl], alpha subunit-<0.1[0.1-0.5ng/ml], ACTH-32[6-20pg/ml], 24-hour urine cortisol-13.7mcg/ 24hr [4-50 mcg/24hr]. Visual field studies showed nasal hemianopia in the right eye. Based on the above labs this pituitary adenoma is likely non-secretory. The patient underwent transsphenoidal surgery in November 2024. Pathology was consistent with tumor cells positive for INSM1, synaptophysin, and chromogranin. The KI-67 index is approximately 2%. Reticulin special stains showed disruption of the reticulin network. All consistent with pituitary neuroendocrine tumor (Pit NET/adenoma). He had a second transsphenoidal endoscopic resection of the pituitary tumor on December 3, 2024, due to a residual lesion. Labs after the second surgery (Jan 2025): Total testosterone <1, free testosterone undetectable, LH <0.3, FSH <0.3, TSH 0.11, free T4-0.9, prolactin 1.5, ACTH <5 - Indicating panhypopituitarism. Conclusion: This case demonstrates an unusual presentation of pituitary adenoma with only gynecomastia and erectile dysfunction, despite multiple pituitary hormone imbalances, and without other symptoms. It is crucial to perform a comprehensive diagnostic workup for unexplained gynecomastia. Presentation: Monday, July 14, 2025